25220

Appears in sequences

• a(n) = Sum_{k=0..n} (k+1) * A026648(n,k).at n=11A026975
• Number of different energy states of n positive and n negative charges on a necklace. Different sets of distances between n points chosen from 2n equally spaced points on a circle.at n=12A045611
• Numbers n such that 1n1, 3n3, 7n7 and 9n9 are all primes.at n=34A059677
• Numbers k such that (2^67 - 1) * 10^k + (2^257 - 1) is prime.at n=7A119650
• Smaller side not divisible by 37 of right triangles with integer sides and integer side inscribed squares with two vertices on the hypotenuse.at n=27A123697
• Eigentriangle by rows, A143971 * (A108300 * 0^(n-k)); 1<=k<=1.at n=53A143972
• a(0)=0 and a(n+1) = 3*a(n) + 2^(n+2).at n=8A145563
• Triangle of coefficients of polynomials v(n,x) jointly generated with A210743; see the Formula section.at n=50A210744
• Number of terms k such that difference between halving and tripling steps in Collatz (3x+1) trajectory of k is n.at n=26A213678
• Smallest even number k such that lpf(k-3) = prime(n) while lpf(k-1) > lpf(k-3), where lpf=least prime factor (A020639).at n=34A242490
• Smallest even k such that the pair {k-3,k-1} is not a twin prime pair and lpf(k-1) > lpf(k-3) >= prime(n), where lpf = least prime factor (A020639).at n=34A242720
• Least even k such that sfdf(k-1) > sfdf(k-3) >= A050376(n), where sfdf(n) is the smallest Fermi-Dirac factor of n (A223490), and k-3 is not the lesser of a pair of Fermi-Dirac twin primes (A229064).at n=41A244412
• a(n) = n*(3*n^2 + 3*n + 1).at n=20A249354
• Number of (n+2)X(3+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 1 2 or 4.at n=4A252060
• Number of (n+2)X(5+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 1 2 or 4.at n=2A252062
• T(n,k)=Number of (n+2)X(k+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 1 2 or 4.at n=23A252065
• T(n,k)=Number of (n+2)X(k+2) 0..2 arrays with every 3X3 subblock row, column, diagonal and antidiagonal sum not equal to 1 2 or 4.at n=25A252065
• Practical numbers z such that z^2 = x^2 + y^2 for some practical numbers x and y with gcd(x,y,z) = 4.at n=36A294112
• Sum of the prime parts in the partitions of n into 9 parts.at n=35A309470
• Numbers k such that phi(k) and phi(k+1) are perfect powers (A001597).at n=45A332008